Thread: Poyurethane glues

Originally Posted by TP1

I know that Poly and water don't mix hence the previous post. I would think it wouldn't take much moisture to weaken the bond. However like others on this forum, I am using Titebond III but so far I can't tell any difference with it and PVA after the projects have been completed.

As far as specific glue failures go, I think you will find if you did a search there will be failures reported with PVA based glues as well. Poly-U glues haven't been around as long as PVA -based ones and it seems we are still learning about their limitations. For me, I will always try to use what the pro's do - they have all the training, experience, successes and failures to learn from.

You don't want to get me started on the chemistry of glues! Polyurethane glue requires water as a catalyst. I followed the manufacturers instruction to the letter regards wiping with a damp rag.

Cheers
Michael

Originally Posted by TP1

Apart from specific applications, the variable element to a good joint should not, I would have thought, be the choice of glue.

are you saying what I think you're saying?

Cheers
Michael

Originally Posted by TP1

There has to be something different about what you are doing or perhaps the particular application. I have done some of my own crude testing with PVA and in each case, the break was never along the glue-line.

If you are doing laminations which are expected to be flexible, perhaps different glues will behave differently. Apart from specific applications, the variable element to a good joint should not, I would have thought, be the choice of glue.

I have only ever done laminations with epoxy. I was told that was the stuff, so that is what I used. If I could use PVA that would be awesome as the stink factor is much lower. However, repetitive bending is not your usual glue joint! As for the other tests, I have been in a situation a few times where I didn't want something that I had glued together connected anymore. With PolyU I tend to break the pieces. With PVA the glue line comes apart nicely. One thing that I possibly do wrong is clamp too hard? I do rather clamp like there is no tomorrow...

Finally, while complaining about my gluing deficiencies - has anyone ever had a contact glue work before? i.e. one of the ones where you cover both pieces, leave it to tack dry then put the bits together? I have never had any luck with that.

Maybe glues just hate me.

Originally Posted by mic-d

You don't want to get me started on the chemistry of glues! Polyurethane glue requires water as a catalyst. I followed the manufacturers instruction to the letter regards wiping with a damp rag.

Cheers
Michael

In the presence of moisture, poly-U glues will expand and foam, quite apart from going off quicker. In view of this, I have viewed Poly-U glues as being suitable where you need expansion to fill any form of irregularity in the joint.

While the glue does need moisture to cure, there is sufficient moisture in the atmosphere and indeed the timber for this purpose, particularly for clean flat surfaces.

Originally Posted by mic-d

are you saying what I think you're saying?

Cheers
Michael

No Michael, I am not.

I was referring to other factors such as temperature, etc. There have been several reported cases of glue failure on this and other forums with a common element of cold temperatures. I thought that there could also be other factors about the type of joint, timber etc that is not obvious from your posts.

I would have thought everyone's technique would have been similar ie prepare perfectly flat and clean surfaces, apply glue to all surfaces liberally, clamp tightly for as long as is practicable, and do not apply any load for at least 24 hours.

Originally Posted by CameronPotter

Finally, while complaining about my gluing deficiencies - has anyone ever had a contact glue work before? i.e. one of the ones where you cover both pieces, leave it to tack dry then put the bits together? I have never had any luck with that.

Hot melt glue works well for this purpose.

I think you thought I thought your thinking was other than it was. What was I thinking?

Cheers
Michael

Originally Posted by TP1

No Michael, I am not.

I was referring to other factors such as temperature, etc. There have been several reported cases of glue failure on this and other forums with a common element of cold temperatures. I thought that there could also be other factors about the type of joint, timber etc that is not obvious from your posts.

I would have thought everyone's technique would have been similar ie prepare perfectly flat and clean surfaces, apply glue to all surfaces liberally, clamp tightly for as long as is practicable, and do not apply any load for at least 24 hours.

Originally Posted by TP1

While the glue does need moisture to cure, there is sufficient moisture in the atmosphere and indeed the timber for this purpose, particularly for clean flat surfaces.

Your thoughts are noted. As I said earlier I have been using polyurethane glue other than Titebond for the better part of 7 years without a failure. Have always followed the manufacturers instructions and wiped the surface with a damp cloth. The advice to follow comes from the one's who've done the testing ie the manufacturers, I would have thought. Especially if one wants to query the company on the product. Could you imagine the call, 'well sir did you follow the intructions, did you dampen the joint? well er no, I heard it wasn't needed. Click.. beep beep beep...' Actually this is the first glue failure I've ever had with any glue period. So thanks, but I'll keep doing it their way until they tell me otherwise, just not with Titebond poly.

Cheers
Michael

I had a rep out from one of the glue companies a few years ago when I was looking for a glue to fix light aluminium sheet to plywood.

I can buy commercilay produced product like this & it seems the glue they use is poly U.

anyway.... buggered if I could get the stuff to bond half as well as sprayable contact cement.

I had a long chat with the rep about the polyU....& yes he said that moisture was required for a cure.....but he said that almost without exception there is enough moisture in commercilay produced timber.

We discussed if it was necessary to damp the aluminium...& I tried a number of ways.....& just gave up on the whole thing because the contact glue was working just fine.

A couple of things occur to me.
If the timber has been moistened..and remains moist on the surface this may interfeer with the glue gaining access to the timber a barrier if you like

If the timber has been surfaced with a hand plane ( I assume that it will be sharp and well tuned) the surface may be too smooth..particularly if it is a tight or oily hardwood

If the pieces have been very well fitted....even moderate clamping may be sufficient to starve the joint of glue.

or perhaps a combination of the above.

Is there any further news


As for contact cement working....yep I have used a lot of it...and yeh treat it right and get it at the right moment and it sticks realy well.... often too well.....I have.been laying up laminate on plywood and not got it straight......too bad its stuck now......but there are a variety of reasons why you can have bond failures with contact cement.

This is the problem with lots of the instructions for glues...they say do this ..... but they don't give you much detail or information about possible reasons for joint failures............Yeh I did that... but was it too much , not enough, too early, too late or just not appropriate in this situation....ya just don't know without some further guidance or a heap of experiments.

ages ago I borrowed a book from our local library on using laminates ( like formica and laminex)...it gave a whole list of reasons for contact glue failure in laminates....& I had experienced several of them and wondered why......it was the best thing

If there is a similar thing on poly U... that would be a great thing.

cheers

The rubberised polyurethane sealant glues appear to be waterproof and work well according to these tests - not sure why he didn't include a foamy polyurethane glue or something similar.

Construction glue for boatbuilding?

Unfortunately these glues do not look too flash so are only suitable if you are going to paint or if they are not going to show, or you really don't give a damn. The ones I have used are extremely rubbery and are extremely unlikely to suffer from the shattering effect some hav ecomplained of with PVAs or the foamy stuff.

I have used the mesh and goo method (gyprock jointing tape and polyurethane) on a couple of my throw away boats and they are holding together extremely well.

I have used the Vise polyurethane foamy glue which seems to have worked reasonably well in repairing old unstuck joints in chairs and gluing the wood together on my throw away boats. The only spots where It has given way has been where a wood to thin plywood allowed the movement to stress the edge most (like ripping off a bandaid kind of and in a fairly high stress join on the floor of one of my boats - possibly just due to the cheap plywood.